I ran CrystalDiskMark on my Surface Go (8 GB/128 GB, Windows 10 Pro) and Surface 3 (4 GB/128 GB, Windows 8.1 Pro) to compare:
internal C drive
SanDisk 32 GB micro SDXC card (not sure the speed, but over 3 years old)
Samsung EVO Select 128 GB micro SDXC card
I have been perfectly happy with my Surface 3 for the three-plus years I've used it, other than it being too big. Given that it has been plenty fast enough for the tasks for which I use it, I expect to be very happy with the Go's speed.

internal C drive
SanDisk 32 GB micro SDXC card (not sure the speed, but over 3 years old)
Samsung EVO Select 128 GB micro SDXC card
I have been perfectly happy with my Surface 3 for the three-plus years I've used it, other than it being too big. Given that it has been plenty fast enough for the tasks for which I use it, I expect to be very happy with the Go's speed.
